This invention is generally directed to imaging members for electrographic applications, and more specifically, the present invention is directed to photoconductive imaging members comprised of silicon and silicon oxide. Therefore, in one embodiment of the present invention, there is provided a photoresponsive imaging member comprised of a supporting substrate and in contact therewith a photogenerating and charge transport layer comprised of islands of hydrogenated amorphous silicon, or crystalline silicon present in a silicon oxide matrix containing at least 50 atomic percent of oxygen. More specifically, in one embodiment of the present invention there is provided an imaging member comprised of a supporting substrate in contact therewith, and adhering thereto a layer comprising a photogenerating substance, such as hydrogenated amorphous silicon, or crystalline silicon dispersed in charge transporting molecules, preferably comprised of silicon oxides formulated by plasma deposition, and containing at least 50 atomic percent of oxygen. The aforementioned imaging members can be incorporated into electrophotographic, and in particular xerographic imaging and printing systems wherein, for example, the formed latent electrostatic patterns are developed into images of high quality and excellent resolution. Moreover, the imaging members of the present invention possess high charge acceptance values corresponding to electric fields in excess of 50 volts per micron (50 volts/.mu.m); and further these members can be of a very desirable thickness of from, for example, about 100 microns or less. Also, the imaging members of the present invention have desirable low dark decay and high cyclic stability properties enabling them to be particularly useful in xerographic imaging processes. In these processes, latent electrostatic images are formed on the imaging members illustrated herein, followed by development, transfer and fixing. Additionally, the photoresponsive imaging members of the present invention, when incorporated into xerographic imaging and printing systems, are insensitive to (1) humidity, of from, for example, 20 to 80 percent, and (2) corona ions permitting the formation of acceptable images of high resolution for an extended number of imaging cycles. Furthermore, the photoresponsive imaging members of the present invention which can be charged and photodischarged for negative, or positive polarities possess superior mechanical wear characteristics.
Electrostatographic imaging, particularly xerographic imaging processes, are well known, and are extensively described in the prior art. In these processes a photoconductor material is selected for forming latent electrostatic images thereon. The photoconductor is generally comprised of a conductive substrate containing on its surface a layer of photoconductive material; and in many instances, a thin barrier layer is situated therebetween to prevent charge injection from the substrate which injection could adversely effect the quality of the resulting image. Examples of known useful photoconductive materials include amorphous selenium, alloys of selenium such as selenium-tellurium, selenium-arsenic, and the like. Additionally, there can be selected as photoresponsive imaging members various organic photoconductive materials including, for example, complexes of trinitrofluorenone and polyvinylcarbazole. There are also disclosed layered organic photoresponsive devices with aryl amine hole transporting molecules, and photogenerating layers, reference U.S. Pat. No. 4,265,990, the disclosure of which is totally incorporated herein by reference.
Also known are amorphous silicon photoconductors, reference for example U.S. Pat. No. 4,265,991. There is disclosed in the '991 patent an electrophotographic photosensitive member comprised of a substrate, and a photoconductive overlayer of amorphous silicon containing 10 to 40 atomic percent of hydrogen with a thickness of 5 to 80 microns. Additionally, this patent describes several processes for preparing amorphous silicon members. In one process embodiment, there is prepared an electrophotographic photosensitive member by heating the member present in a chamber to a temperature of 50.degree. C. to 350.degree. C., thereafter introducing a gas with silicon and hydrogen atoms, providing an electrical discharge in the chamber by electric energy to ionize the gas, followed by depositing amorphous silicon on an electrophotographic substrate at a rate of 0.5 to 100 Angstroms per second by utilizing an electric discharge thereby resulting in an amorphous silicon photoconductive layer of a predetermined thickness. Although the amorphous silicon device described in this patent is photosensitive, after a minimum number of imaging cycles, less than about 100 for example, unacceptable low quality images of poor resolution with many deletions may result. With further cycling, that is subsequent to 100 imaging cycles and after 1,000 imaging cycles, the image quality may continue to deteriorate, often until images are completely deleted.
Further, there are disclosed in the prior art amorphous silicon photoreceptor imaging members containing, for example, stoichiometric silicon nitride overcoatings; however, these members in some instances generate prints of low resolution as a result of the electric field induced lateral conductivity in the photogenerator layer. Additionally, with the aforementioned silicon nitride overcoatings, the resolution loss can in many instances be extreme thereby preventing, for example, any image formation whatsoever.
Other representative prior art disclosing amorphous silicon imaging members, including those with overcoatings, are U.S. Pat. Nos. 4,460,669; 4,465,750; 4,394,426; 4,394,425; 4,409,308; 4,414,319; 4,443,529; 4,452,874; 4,452,875; 4,483,911; 4,359,512; 4,403,026; 4,416,962; 4,423,133; 4,460,670; 4,461,820; 4,484,809; and 4,490,453. Additionally, U.S. patents that may be of background interest with respect to hydrogenated amorphous silicon photoreceptor members include, for example Nos. 4,377,628; 4,420,546; 4,471,042; 4,477,549; 4,486,521; and 4,490,454.
Further, additional representative prior art patents that disclose amorphous silicon imaging members include, for example, 4,357,179 directed to methods for preparing imaging members containing high density amorphous silicon or germanium; 4,237,501 which discloses a method for preparing hydrogenated amorphous silicon wherein ammonia is introduced into a reaction chamber 4,359,514; 4,404,076; 4,397,933; 4,423,133; 4,461,819, 4,237,151; 4,356,246; 4,361,638; 4,365,013; 3,160,521; 3,160,522; 3,496,037; 4,394,426; and 3,892,650. Of specific interest are the amorphous silicon photoreceptors illustrated in U.S. Pat. No. 4,510,224, which discloses an electrophotographic photoreceptor comprising a hydrogenated amorphous silicon carbide transport layer 2 formed below a photoconductive layer 3, reference FIG. 5; 4,518,670 directed to an electrophotographic member comprising a transport layer 2 with at least one atomic percent nitrogen present therein, see FIGS. 1 to 4; and 4,495,262 describing an electrophotograpic photosensitive member comprising two amorphous hydrogenated silicon carbide layers 2 and 4, one on each side of the photoconductive layer 3, reference FIGS. 1 and 2. Additionally, processes for depositing large area defect free films of amorphous silicon by the glow discharge of silane gases are described by Chittick et al., the Journal of the Electrochemical Society, Volume 116, Page 77, (1969). Further, the fabrication and optimization of substrate temperatures during amorphous silicon fabrication is illustrated by Walter Spear, the Fifth International Conference on Amorphous and Liquid Semiconductors presented at Garmisch Partenkirchen, West Germany in 1963. Other silicon fabrication processes are described in the Journal of Non-Crystalline Solids, Volumes 8 to 10, Page 727, (1972), and the Journal of Non-Crystalline Solids, Volume 13, Page 55 (1973).
In addition, other prior art of interest includes U.S. Pat. No. 4,557,987, which discloses forming a film by the reaction of a silane and nitrous oxide, reference column 7; and an article by C. E. Morosanu, entitled Thin Film Preparation By Plasma and Low Pressure CVD In A Horizontal Reactor, wherein there is illustrated the formation of silicon, silicon oxide, and sliicon nitride films by chemical vapor deposition. Also, other references of background interest relating to hydrogenated amorphous silicon imaging members include U.S. Pat. Nos. 4,217,374; 4,237,150; 4,237,151; 4,565,731; 4,613,556; and 4,615,905.
There are also illustrated in other patents photoconductive imaging members comprised of amorphous silicon. Accordingly, for example, there is illustrated in U.S. Pat. No. 4,634,647 entitled Electrophotographic Devices Containing Compensated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, an imaging member comprised of a supporting substrate and an amorphous hydrogenated silicon composition containing from about 25 parts per million by weight to about 1 percent by weight of boron compensated with substantially equal amounts of phosphorus. Furthermore, there is described in U.S. Pat. No. 4,544,616 entitlted Electrophotographic Devices Containing Overcoated Amorphous Silicon Compositions, the disclosure of which is totally incorporated herein by reference, imaging members comprised of a supporting substrate, an amorphous silicon layer, a trapping layer comprised of doped amorphous silicon, and a top overcoating layer of stoichiometric silicon nitrides. More specifically, there is disclosed in this patent an imaging member comprised of a supporting substrate; a carrier transport layer comprised of uncompensated or undoped amorphous silicon; or amorphous silicon slightly doped with p or n type dopants such as boron or phosphorus; a thin trapping layer comprised of amorphous silicon which is heavily doped with p or n type dopants such as boron or phosphorus; and a top overcoating layer of silicon nitride of specific compositions, silicon carbide, or amorphous carbon. However, one disadvantage with this imaging member is that the trapping layer introduces a dark decay component which reduces the charge acceptance for the imaging member.
Additionally, described in copending application U.S. Pat. No. 4,613,556, entitled Heterogeneous Electrophotographic Imaging Members of Amorphous Silicon, the disclosure of which is totally incorporated herein by reference, are imaging members comprised of hydrogenated amorphous silicon photogenerating compositions, and a charge transporting layer of plasma deposited silicon oxide containing at least 50 atomic percent of oxygen. Moreover, there are disclosed in copending application U.S. Pat. No. 4,737,429, relating to amorphous silicon imaging members, the disclosure of which is totally incorporated herein by reference, photoresponsive imaging members comprised of a supporting substrate; a photoconductive layer of hydrogenated amorphous silicon in contact therewith; and a charge transport layer comprised of components selected from the group consisting of hydrogenated or halogenated silicon nitrides, boron nitrides, aluminum nitrides, phosphorus nitrides, gallium nitrides, gallium phosphides, boron phosphides, aluminum phosphides, boron oxide, aluminum oxide, gallium oxide, and plasma deposited organosilanes. Furthermore, the photoresponsive imaging members of the aforementioned copending application can contain a top protective overcoating layer; and the charge transport layer can be situated between the photoconductive layer of hydrogenated amorphous silicon, and the supporting substrate; or alternatively, is in contact with the photoconductive layer situated between the supporting substrate, and the charge transport layer.
Although the above described amorphous silicon photoresponsive members, particularly those disclosed in the copending applications and Xerox patents are suitable for their intended purposes, there continues to be a need for improved members comprised of silicon and silicon alloys. Additionally, there is a need for silicon based imaging members that possess desirable high charge acceptance values, low charge loss characteristics in the dark, improved adhesion characteristics, excellent transport of electrical charges, and improved cyclic stability. Furthermore, there continues to be a need for improved silicon based imaging members, with specific charge transport layers. Also, there is a need for silicon based imaging members with transport layers of silicon oxide containing spatially distributed photoconductive regions of silicon or hydrogenated amorphous silicon or other silicon alloys, thereby enabling members with superior mechanical wear characteristics. Abrasive wear of members with the aforementioned spatially distributed photoconductive regions do not evidence an abrupt failure mode due to the wear of the discrete photoconductive layer, but rather retain their photoconductive properties during the imaging process. Further, there is a need for imaging members with the aforementioned charge transport layers, and where there is introduced therein, by the compositional control of constitutent materials, electronic defect states of sufficient density enabling transport to be accomplished by hopping between the resulting localized states. These states are energetically positioned in the band gap of the charge transport component to permit the efficient injection of carriers from the silicon photogenerating regions. Furthermore, there is a need for silicon based imaging members with the properties of low surface potential decay rates in the dark, and photosensitivity in the visible and the near visible wavelength range. Also, there is a need for imaging members with improved charge transport characteristics thereby permitting the residual voltage after optical exposure to be of a relatively small value, that is from about 0 volts to about 10 volts, which voltage remains substantially constant upon repeated cycling of the imaging member.